Zan Zhang

Bio: Zan Zhang is an academic researcher from Chang'an University. The author has contributed to research in topics: Grating & Silicon photonics. The author has an hindex of 10, co-authored 47 publications receiving 239 citations. Previous affiliations of Zan Zhang include Chinese Academy of Sciences.

CMOS-Compatible Vertical Grating Coupler With Quasi Mach–Zehnder Characteristics

Abstract: A vertical grating coupler on silicon-on-insulator substrates has been designed and demonstrated. The light from a vertical fiber can be coupled in and split equally into two arms with the fiber placed in the grating center. An optical combiner is used to collect the transmission from the two arms. The measured peak coupling efficiency is 37%. Our device can also function like a Mach-Zehnder interferometer. In a device with an arm difference of 30 μm, the normalized transmission spectra of 20-nm free spectral range and more than 12-dB extinction ratio at 1567 nm are obtained.

A graphene based frequency quadrupler

Abstract: Benefit from exceptional electrical transport properties, graphene receives worldwide attentions, especially in the domain of high frequency electronics. Due to absence of effective bandgap causing off-state the device, graphene material is extraordinarily suitable for analog circuits rather than digital applications. With this unique ambipolar behavior, graphene can be exploited and utilized to achieve high performance for frequency multipliers. Here, dual-gated graphene field-effect transistors have been firstly used to achieve frequency quadrupling. Two Dirac points in the transfer curves of the designed GFETs can be observed by tuning top-gate voltages, which is essential to generate the fourth harmonic. By applying 200 kHz sinusoid input, arround 50% of the output signal radio frequency power is concentrated at the desired frequency of 800 kHz. Additionally, in suitable operation areas, our devices can work as high performance frequency doublers and frequency triplers. Considered both simple device structure and potential superhigh carrier mobility of graphene material, graphene-based frequency quadruplers may have lots of superiorities in regards to ultrahigh frequency electronic applications in near future. Moreover, versatility of carbon material system is far-reaching for realization of complementary metal-oxide-semiconductor compatible electrically active devices.

Microwave photonic filter with reconfigurable and tunable bandpass response using integrated optical signal processor based on microring resonator

Abstract: A bandpass microwave photonic filter based on an integrated optical signal processor is proposed and demonstrated by numerical sim- ulation. The optical signal processor consisting of double-bus-coupled and series-cascaded silicon microrings (MRs) is used to produce two bandpass responses to process optical carrier signal and sideband signal separately. Because of the tunability of MRs, variable −3 dB bandwidth and tunable operating frequency are achieved. The −3 dB bandwidth and operating frequency can be tuned from 1.5 to 12 GHz and from 15 to 34 GHz, respectively. The loss impact, tuning method, and fabrication error tolerance are also discussed. © 2013 Society of Photo-Optical Instrumentation

Frequency conversion with nonlinear graphene photodetectors.

Abstract: Frequency conversion with nonlinear electronic components, a common approach for signal processing required in various communication applications, has found its operation bandwidth bottleneck due to the limited carrier mobility of the traditional materials. Meanwhile, fiber-optics communications are playing a significant role in communication services due to their excellent signal transmission properties. However, the transmitted optical signals had to be converted to electrical signals with photodetectors before frequency conversion was performed through conventional electronic devices, which make this conversion system very complex and costly. Hence, to develop a compact device that can achieve the photodetection and frequency conversion functions simultaneously is critical and significative. Here, we have proposed a novel concept for frequency conversion and demonstrated a nonlinear graphene photodetector based frequency converter that performs frequency conversion from optical signals directly. With this new concept, a frequency doubling signal at 4 GHz was obtained from a 2 GHz intensity-modulated optical signal. Moreover, using a 10 MHz intensity-modulated optical signal and another 3 GHz intensity-modulated optical signal, we show the frequency up-conversion to 3 ± 0.01 GHz. In particular, the frequency down-conversion to 100 MHz was achieved successfully by using a 2 GHz intensity-modulated optical signal and another 2.1 GHz intensity-modulated optical signal. Considering the broadband optical absorption, strong saturable absorption, high carrier mobility, and short photogenerated carrier lifetime of the graphene material, graphene photodetectors have the potential to achieve the frequency conversion of millimeter-wave band, which will open promising prospects in the domain of microwave photonics for next-gen communication systems.

Optoelectronic Mixer Based on Graphene FET

Abstract: We present optoelectronic mixing phenomenon in graphene FET (GFET) and give a brief analysis for the first time. Demonstrated by a measurement system, two operating modes of optoelectronic mixer (OE-mixer) circuits are proposed, either of them mixing optical and electrical signals directly using a single GFET. Optoelectronic conversion losses of 24 and 35 dB are obtained in a 50-Ω impedance system, respectively. GFET OE-mixer might be of strong importance for radio over fiber systems, millimeter wave, and terahertz frequencies applications.

Graphene and two-dimensional materials for silicon technology.

Abstract: The development of silicon semiconductor technology has produced breakthroughs in electronics—from the microprocessor in the late 1960s to early 1970s, to automation, computers and smartphones—by downscaling the physical size of devices and wires to the nanometre regime. Now, graphene and related two-dimensional (2D) materials offer prospects of unprecedented advances in device performance at the atomic limit, and a synergistic combination of 2D materials with silicon chips promises a heterogeneous platform to deliver massively enhanced potential based on silicon technology. Integration is achieved via three-dimensional monolithic construction of multifunctional high-rise 2D silicon chips, enabling enhanced performance by exploiting the vertical direction and the functional diversification of the silicon platform for applications in opto-electronics and sensing. Here we review the opportunities, progress and challenges of integrating atomically thin materials with silicon-based nanosystems, and also consider the prospects for computational and non-computational applications. Progress in integrating atomically thin two-dimensional materials with silicon-based technology is reviewed, together with the associated opportunities and challenges, and a roadmap for future applications is presented.

「レイリー散乱」(Rayleigh Scattering)

Abstract: • Rayleigh scattering is an approximation used to predict scattering from particles much smaller than an electromagnetic wavelength • The approximation is based on quasi-static ideas: in regions of space much smaller than a wavelength, fields act approximately like static fields • Basic procedure: solve statics problem to determine field inside scatterer when a uniform field (plane wave) impinges from outside • This determines field inside particle so we can then compute scattering cross sections, etc, using our previous equations • This is a nice method because we have lots of analytical techniques for solving the Laplace equation, also usually will predict constant fields inside scatterer

Gate-Variable Optical Transitions in Graphene

Abstract: Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be substantially modified through electrical gating, much like electrical transport in field-effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, whereas in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability by simple electrical gating hold promise for new applications in infrared optics and optoelectronics.

Coupling light in photonic crystal waveguides: A review

Abstract: Submicron scale structures with high index contrast are key to compact structures for realizing photonic integrated structures. Ultra-compact optical devices in silicon-on-insulator (SOI) substrates serve compatibility with semiconductor fabrication technology leading to reduction of cost and mass production. Photonic crystal structures possess immense potential for realizing various compact optical devices. However, coupling light to photonic crystal waveguide structures is crucial in order to achieve strong transmission and wider bandwidth of signal. Widening of bandwidth will increase potential for various applications and high transmission will make easy signal detection at the output. In this paper, the techniques reported so far for coupling light in photonic crystal waveguides have been reviewed and analyzed so that a comprehensive guide for an efficient coupling to photonic crystal waveguides can be made possible.

ZnO Nanowire-Reduced Graphene Oxide Hybrid Based Portable NH 3 Gas Sensing Electron Device

Abstract: A ZnO nanowire-reduced graphene oxide (ZnO-rGO) based portable ammonia (NH3) gas sensing electron device working at room temperature has been demonstrated for the first time. The sensor is developed on a microelectrode of micro-electromechanical systems and supported by peripheral circuits and a hosting computer, which enables the real-time detection of NH3 at room temperature. In contrast to the traditional sensors based on pure graphene or ZnO nanowires alone, the ZnO-rGO based gas sensing electron device can detect low-concentration (1 ppm) NH3 with higher sensitivity ( $\sim 7.2$ %). Besides, this sensor exhibits satisfying properties at sensing NH3 with the concentration as low as 500 ppb at room temperature.